Viessmann vitopend 100 - Hot water issue: water is only lukewarm on maximum

[Jamesbo]

Dear All,

please help me. My Viessmann vitopend 100 has a hot warm issue. Yesterday we had hot water, but today it is lukewarm, and only on the maximum setting. If I reset it to medium, the flame does not come on. Has anyone ever had this problem? Which part do you think I should replace? Thank you for your help.

 

[Murdochcat]

You need a GSR

 

[Jamesbo]

Thank You for your answer. My gsr is only 1 year old. It is as if the hot water temperature sensor has failed and is giving false readings, or the hot water temperature controller. What are these sensors, what are their names? The heating is working fine, it is already giving hot water to the radiators on setting 3. Thank you in advance!